It has been a long standing problem in distributed line networks to detect the location of a ground fault (i.e., single-line-to-ground fault) in the network in a cost effective and efficient manner. For example, in a three-phase system wherein three-phase power lines are provided to a plurality of three-phase loads throughout the distributed line network, a ground fault may occur on any of the three phases. Conventional detection of the existence of the ground fault typically entails an operator modulating the ground (neutral phase) line of the network through a large resister. If the modulated signal is detected in one of the other three phases, the operator concludes that the phase having the modulated signal is the phase which is ground faulted. The operator then proceeds to search throughout the entire system to determine where the ground fault may have occurred. Various tools are used for this part of the procedure; for example, signals are often sent down the power lines and their reflection is measured to determine how far into the system network the ground fault occurred. Known techniques for tracing the location of the ground fault have required significant manual intervention, expensive equipment and/or shutting down parts of the entire network.
Another burdensome technique has been to apply large current transformers which encircle all phase conductors with associated circuit breaker trip units at locations throughout the system. Low level ground faults are sensed at each location and, if desired, the associated trip unit then isolates the fault by "breaking" the phase conductors.
Accordingly, there is a need for a technique which detects the presence of and locates such faults efficiently and without significant manual intervention.